Method for manufacturing small-sized motor

ABSTRACT

A method of the present invention for manufacturing a small-sized motor relates to cutting or grinding of a shaft end portion of a rotor into a noncircular shape over a predetermined length for establishing a mechanical coupling with a device to be driven. The cutting or grinding work is performed after a laminated core  7 , a winding  6 , a commutator  5 , and a thrust bush  8  are assembled on a shaft  11  to thereby assemble the rotor. Alternatively, a process of cutting or grinding the shaft end portion into a noncircular shape is performed after a casing  1 , an end bell  4  to be fitted to an opening portion of the casing  1 , and a rotor are assembled into a small-sized motor. Thus, the present invention provides a method for manufacturing a small-sized motor in which a shaft has a D cut formed thereon, enables determination of whether or not the D cut is to be formed on the shaft, at a later stage of a motor assembly process, to thereby eliminating the need to control the stock of shafts bearing the D cut, does not involve the need to orient shafts in the same direction in preparation for press-fitting of laminated cores of rotors to the corresponding shafts, and can prevent generation of scrapings when a thrust bush is press-fitted to a shaft.

TECHNICAL FIELD

The present invention relates to a method for manufacturing asmall-sized motor in which an end portion of a shaft of a rotor ismachined into a noncircular shape.

BACKGROUND ART

A small-sized motor is used in various fields in order to, for example,adjust an angle of or to retract a motor-driven mirror of a car, or todrive a mechanism of a toy. In such an application, in order toestablish mechanical coupling between a small-sized motor and a gear,for example, of a device to be driven, the following techniques havebeen used conventionally. That is, an end portion of a round shaft ofthe small-sized motor is machined into a noncircular shape (for example,a D shape), while a center hole of the gear for receiving the shaft isformed in a shape (for example, a D shape) corresponding to thenoncircular shape of the shaft end, thereby establishingrelative-rotation-prevention means. Alternatively, an inner bore of acylindrical body for receiving the noncircular shaft end portion isformed in a circular shape, while, for example, a screw is screwed intothe body from outside and perpendicular to the shaft such that an end ofthe screw is pressed against the noncircular portion (a flat portion ofthe D shape) of the shaft end, thereby establishingrelative-rotation-prevention means. Conventionally, an end portion of ashaft of a small-sized motor is ground or cut into a noncircular shapebefore the shaft is assembled in the motor.

FIG. 5 shows a conventional shaft before assembly having a D cut 12formed thereon so as to prevent relative rotation. In FIG. 5, referencenumeral 11 denotes a shaft, and reference numeral 16 denotes an edgeportion of the D cut 12. Herein, the term “D cut” refers to grinding orcutting of an end portion of a round shaft into a noncircular shape,typically, a D shape.

According to a conventional practice for forming a D cut on a shaftbefore assembly through grinding or cutting, about 100 shafts, forexample, are fixedly arranged in a rest jig and are ground by use of arotating grinding wheel. However, this prior art involves the followingdrawbacks.

About 100 shafts are typically ground simultaneously in order to form aD cut thereon. Therefore, grinding shafts in a smaller lot in order tofulfill an order results in a higher machining cost.

The amount of production of motors equipped with a shaft bearing a D cutmust be grasped at the stage of manufacturing shafts. If customer demandshould vary, the stock of shafts might increase beyond a scheduledlevel.

When a laminated core is to be fitted to a shaft bearing a D cut, thelaminated core is press-fitted to the shaft from an end opposite the Dcut (a shaft end not bearing the D cut) in order to avoid the edgeportion 16 of the D cut scraping a bore wall portion of the laminatedcore. Therefore, shafts to be fed to a press-fitting machine forpress-fitting laminated cores to the corresponding shafts must beoriented such that shaft ends on which the D cut is formed face the samedirection.

When a thrust bush produced from brass is press-fitted to a shaft inorder to axially position a rotor, the edge portion 16 of the D cut 12scrapes a bore wall portion of the thrust bush, and scrapings adhere tothe edge portion 16.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method formanufacturing a small-sized motor in which a D cut is formed on a shaft,which method enables determination of whether or not the D cut is to beformed on the shaft, at a later stage of a motor assembly process,thereby requiring no need to control the stock of shafts bearing the Dcut.

Another object of the present invention is to eliminate the need toorient shafts in the same direction in preparation for press-fitting oflaminated cores of rotors to the corresponding shafts.

Still another object of the present invention is to prevent generationof scrapings when a thrust bush is press-fitted to a shaft.

A method of the present invention for manufacturing a small-sized motorcomprises a step of cutting or grinding a shaft end portion of a rotorinto a noncircular shape over a predetermined length for establishing amechanical coupling with a device to be driven, and is characterized inthat the cutting or grinding work is performed after a laminated core 7,a winding 6, a commutator 5, and a strap bush 8 are assembled on a shaft11 to thereby assemble a rotor.

A method of the present invention for manufacturing a small-sized motoris characterized in that a shaft end portion of a rotor is cut or groundinto a noncircular shape for establishing a mechanical coupling with adevice to be driven, after a casing 1, an end bell to be fitted to anopening of the casing 1, and a rotor are assembled into the small-sizedmotor.

Thus, the present invention does not involve stock control of shaftsbearing a D cut, need to orient the shafts such that their D-cut endsface the same direction when laminated cores of rotors are to bepress-fitted to the corresponding shafts, or generation of scrapingswhen thrust bushes are press-fitted to the corresponding shafts.

The shaft end portion can be cut by combined use of a punch 14 and a die13 having a hole formed therein for receiving the shaft end portion.

The punch 14 to be used in combination with the die 13 may be steplessor may have a plurality of steps and can cut the shaft end portion in asingle stroke.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a rotor of a small-sized motor for explaining afirst embodiment of the present invention in which a D cut is formed ona shaft end portion after the rotor is assembled;

FIG. 2 is a partially sectional view showing a small-sized motor forexplaining a second embodiment of the present invention in which a D cutis formed on a shaft end portion after the small-sized motor isassembled;

FIG. 3 is a view showing a die and a punch for explaining a method ofthe present invention for forming a D cut on a shaft;

FIG. 4 is an enlarged view showing an end portion of a punch for use incutting a D cut; and

FIG. 5 is a view showing a conventional shaft before assembly having a Dcut formed thereon and adapted to prevent relative rotation.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will next be described withreference to the drawings. FIG. 1 shows a rotor of a small-sized motorand represents a first embodiment of the present invention in which a Dcut is formed on a shaft end portion after the rotor is assembled. InFIG. 1, reference numeral 5 denotes a commutator; reference numeral 6denotes a winding; reference numeral 7 denotes a laminated core forestablishing magnetic poles; reference numeral 8 denotes a thrust bushproduced from brass; reference numeral 11 denotes a shaft; and referencenumeral 12 denotes a D cut.

The rotor is a conventional one except that the D cut 12 is formed onthe shaft 11, and can be assembled according to a conventional processexcept that the D cut is formed. The laminated core 7 is press-fitted tothe shaft 11 on which the D cut is not formed, by use of a press-fittingmachine. Next, the commutator 5 is fitted to the shaft 11. Subsequently,the winding 6 is wound on the laminated core 7 to thereby form magneticpoles of the rotor. End portions of the winding are, for example,soldered or spot-welded to members extending from the correspondingcommutator segments, thereby establishing electrical and mechanicalconnection therebetween. At the final stage of assembling the rotor, thethrust bush 8 of brass is press-fitted to the shaft 11 from an endopposite the commutator 5 to thereby position the rotor axially. At thisstage, the D cut is not formed on the shaft 11; therefore, the thrustbush is not scraped. Subsequently, the D cut 12 is formed on an endportion of the shaft 11 over a predetermined length required formechanical coupling with a device to be driven, by use of a die, whichwill be described later. As described above, according to the firstembodiment, the D cut is formed on an end portion of the shaft 11 afterthe rotor is assembled.

FIG. 2 is a view for explaining a second embodiment of the presentinvention. According to the second embodiment, the D cut is formed on ashaft end after a small-sized motor is assembled. In FIG. 2, referencenumeral 1 denotes a casing of the small-sized motor; reference numeral 2denotes a pair of bearings located at opposite sides of the small-sizedmotor and fitted to the shaft 11; reference numeral 3 denotes a brush;and reference numeral 4 denotes an end bell.

The small-sized motor of the present embodiment is a conventional oneexcept that the D cut 12 is formed on the shaft 11, and can be assembledaccording to a conventional process. The casing 1 is produced from ametallic material and is formed into a closed-bottomed cylindricalshape. Permanent magnets are fixedly attached to an innercircumferential surface of the casing 1. The end bell 4 is fitted to anopening portion of the casing 1 to thereby close the casing 1. The endbell 4 is equipped with the brushes 3 and input terminals 10 connectedelectrically to the brushes 3. One of the paired bearings 2 is locatedat a bottom portion of the casing 1, while the other bearing 2 islocated at a central portion of the end bell 4, thereby supporting therotor in a rotatable manner.

The rotor is assembled in a manner similar to that for the rotor of FIG.1. The small-sized motor is assembled according to a conventionalprocess by use of the rotor in which the D cut is not formed on theshaft 11. Specifically, the assembled rotor is inserted into the metalcasing 1 equipped with the permanent magnets through the opening portionof the casing 1 such that the shaft 11 is inserted into the bearinglocated at the bottom portion of the casing 1. Then, the end bell 4equipped with the brushes 3 and the input terminals 10 is attached tothe casing 1, thereby completing assembly of the small-sized motor.Subsequently, the D cut is formed on a shaft end portion over apredetermined length by use of a die as will be described later. Asdescribed above, according to the second embodiment, the D cut is formedon an end portion of the shaft 11 after the small-sized motor isassembled.

FIG. 3 is a view for explaining a method of forming a D cut on the shaftby combined use of a die and a punch. FIG. 3(a) is a top view, and FIG.3(b) is a sectional view taken along line A—A of FIG. 3(a). In FIG. 3,reference numeral 11 denotes a shaft; reference numeral 13 denotes adie; and reference numeral 14 denotes a punch.

The die 13 has a hole formed therein horizontally and adapted to receivethe shaft 11. When a D cut is to be formed on the shaft 11, an endportion of the shaft 11 is inserted into the hole formed in the die 13after the rotor is assembled as described previously with reference toFIG. 1 or after the small-sized motor is assembled as describedpreviously with reference to FIG. 2. The shaft 11 is fixed againstrotation at a portion located just outside the hole formed in the die13.

A passage for the punch 14 is formed in the die 13 perpendicularly tothe hole into which the shaft 11 is inserted. The width of the punch 14and the position of the passage are determined such that a D cut havinga predetermined length is formed on an end portion of the inserted shaft11 in a single stroke of cutting when the punch 14 is driven downwardfrom its upper position of stroke by, for example, hydraulic means.

FIG. 4 is an enlarged view of an end portion of the punch 14 used to cutsuch a D cut. When the punch was produced from “hard metal” or “highspeed steel”, and a relatively soft, ferrous shaft (JIS code “SWRH82B”)that contains carbon in an amount of 0.79-0.86% by weight was used, thepunch was able to properly cut the shaft in a single stroke.

FIG. 4(a) shows a stepless punch, and FIG. 4(b) shows a punch having aplurality of steps 15. The stepless punch 14 is of simple structure. Bycontrast, being of complicated structure, the punch 14 having aplurality of steps as shown in FIG. 4(b) can cut a shaft of higherhardness.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, after a rotor ora small-sized motor is assembled, a shaft end portion of the rotor iscut or ground into a noncircular shape for establishing a mechanicalcoupling with a device to be driven. Accordingly, the necessity of thecutting or grinding work can be determined at the latter stage of amotor assembly process, thereby eliminating the need to control thestock of the thus-cut or -ground shafts. Also, there is no need fororienting shafts in the same direction in preparation for press-fittingof laminated cores of rotors to the corresponding shafts. Further,scrapings are not generated during press-fitting of a thrust bush to ashaft.

What is claimed is:
 1. A method for manufacturing a small-sized motor equipped with a rotor in which a laminated core, a winding wound onto the laminated core, a commutator, and a thrust bush are assembled on a shaft, the method comprising the steps of: cutting or grinding a shaft end portion of the rotor into a noncircular shape over a predetermined length for establishing a mechanical coupling with a device to be driven; and prior to said step of cutting or grinding the shaft, assembling the laminated core, the winding, the commutator, and the thrust bush on the shaft to provide an assembled rotor.
 2. A method for manufacturing a small-sized motor according to claim 1, wherein the shaft end portion is cut by combined use of a punch and a die having a hole formed therein for receiving the shaft end portion.
 3. A method for manufacturing a small-sized motor according to claim 2, wherein the punch used in combination with the die is stepless or has a plurality of steps, and is adapted to cut the shaft end portion in a single stroke.
 4. A method for manufacturing a small-sized motor, the method comprising the steps of: assembling into a unit a rotor having a laminated core, a winding wound onto the laminated core, a commutator, and a thrust bush on a shaft; equipping a casing having an opening portion with a magnet; fitting a bearing to the casing; inserting the shaft of the unit into the bearing; forming a complete assembly by fitting an end bell equipped with brushes and another bearing to the casing and inserting the shaft of the unit into said another bearing; subsequent to said step of forming said complete assembly, cutting or grinding a shaft end portion of the rotor into a noncircular shape over a predetermined length for establishing a mechanical coupling with a device to be driven.
 5. A method for manufacturing a small-sized motor according to claim 4, wherein the shaft end portion is cut by combined use of a punch and a die having a hole formed therein for receiving the shaft end portion.
 6. A method for manufacturing a small-sized motor according to claim 5, wherein the punch used in combination with the die is stepless or has a plurality of steps, and is adapted to cut the shaft end portion in a single stroke.
 7. A method for manufacturing a small-sized motor comprising the steps of: forming a rotor unit by assembling a laminated core, a winding, a commutator, and a thrust bush on a shaft, the shaft of the rotor unit having an extending shaft end portion; providing a die having a hole formed therein for receiving the shaft end portion of the rotor unit; inserting the shaft end portion of the rotor unit into the hole; subsequently cutting, with a punch, the shaft end portion of the rotor unit into a noncircular shape over a predetermined length for establishing a mechanical coupling with a device to be driven.
 8. A method for manufacturing a small-sized motor according to claim 7, further comprising the steps of: equipping a casing having an opening portion with a magnet; fitting a bearing to the casing; inserting the shaft of the rotor unit into the bearing; forming a complete assembly by fitting an end bell equipped with brushes and another bearing to the casing and inserting the shaft of the unit into said another bearing, wherein said step of inserting the shaft end portion of the rotor unit into the hole takes place after said step of forming a complete assembly.
 9. A method for manufacturing a small-sized motor according to claim 8, wherein the shaft end portion is cut by a punch while said shaft end portion of the rotor unit is inserted into the hole of the die.
 10. A method for manufacturing a small-sized motor according to claim 9, wherein the punch used in combination with the die is stepless and is adapted to cut the shaft end portion in a single stroke.
 11. A method for manufacturing a small-sized motor according to claim 9, wherein the punch used in combination with the die has a plurality of steps, and is adapted to cut the shaft end portion in a single stroke. 